Non-video path data collection device

ABSTRACT

A system performs audio matching to determine the channel to which a television set is tuned. In one embodiment, the system feeds two audio signals to primary and secondary windings of an audio transformer, and employs an output signal taken from a center tap on the primary winding to determine whether the audio signals match. In another embodiment, the system detects transitions of the two audio signals, produces a pulse for each transition, and compares the pulses to determine whether the signals match.

RELATED APPLICATIONS

This application is a divisional of U.S. Patent Application Ser. No.08/540,710 filed Oct. 11, 1995 now U.S. Pat. No. 5,881,360.

FIELD OF THE INVENTION

The present invention relates generally to broadcast station audiencemonitoring systems, and more particularly to methods and apparatus formonitoring televisions to determine which channel is being viewed. Theinvention is particularly suited for use in making statistical analysesof the audiences of different transmitting stations. A presentlypreferred embodiment of the invention is especially suited for use withtelevisions receiving CATV signals.

BACKGROUND OF THE INVENTION

The audience monitoring procedures currently used to calculate the sizeof a television and/or radio audience, which determines the pricebroadcasters can charge for advertising time, have come under growingcriticism in recent years. The audience monitoring procedures typicallydepend on responses made by individuals who have agreed to be part of asample audience. To calculate television ratings, for example, viewersare asked to log their time by pressing buttons on a "people meter"attached to their television sets. This method has come under attack bynetwork executives who argue that many of these people simply fail touse the meters. Radio ratings are derived primarily from listeners'diaries, or written logs, and telephone surveys. Television stationscould, of course, employ written logs or telephone surveys. However,written logs require even more discipline from listeners than electroniclogs, and telephone surveys are vulnerable to faulty memories.

U.S. Pat. No. 4,955,070 (Welsh) describes a device that automaticallyidentifies the station tuned in by a listener and logs the amount oftime the listener remains within earshot. The device is based on"acoustic matching," and includes as its key components a microphone, aradio tuner and a micro-processor. The microphone detects sound near theperson being monitored, and the microprocessor converts this sound intoa digital code. The device then compares this code with a codesimilarly-derived from radio stations electronically monitored by thetuner. When the codes from the microphone and the tuner "match," thedevice logs the station and the amount of time the match continues. Animportant feature of this device is that, to determine whether there isa match, the respective signals being compared are first autocorrelatedto determine two sets of correlation coefficients and then the two setsof correlation coefficients are compared. A disadvantage of theautocorrelation technique is that the correlation coefficients will bemodified if the user distorts the frequency spectrum of the broadcastsignal, e.g., by amplifying or suppressing selected frequencycomponents.

French Patent No. 2,555,383 (Barrault) describes a similar audiencemonitoring system, i.e., one that digitalizes the respective signalsbeing compared and then compares the resulting digital signals by way ofa statistical correlation technique.

U.S. Pat. No. 4,388,644 (Ishman et al.), entitled "Apparatus forMonitoring a Multichannel Receiver," discloses a channel-monitoringsystem that includes means for injecting a signal into the antenna inputof the receiver being monitored and means for detecting the injectedsignal at the output of the receiver. The monitor is capable ofdetecting the channel to which the receiver is tuned by varying thefrequency of the injected signal over a prescribed set of frequenciesthat correspond to the channels to which the receiver may be tuned.

Thus, both the Welsh and Barrault techniques involve sophisticateddigital signal processing to determine whether the respective signalsmatch. The Ishman system requires a modification of the input signal ofthe receiver being monitored, which is believed to be too complex andexpensive to be practical. A primary goal of the present invention is toprovide an audience monitoring system that is simpler and more reliablethan the known systems.

SUMMARY OF THE INVENTION

The present invention provides a method and system for determining thechannel to which a television is tuned. In one presently preferredembodiment of the invention, this determination is made by receiving atelevision signal receivable by a television and demodulating thetelevision signal to obtain a first audio signal, and obtaining a secondaudio signal representative of sound generated by the television as aresult of being tuned to one of a prescribed set of channels. A matchsignal is generated on the basis of the first and second audio signals,wherein the match signal indicates whether the first and second audiosignals are from the same television channel. The match signal ispreferably generated by an audio transformer. For example, in thepreferred embodiment, the first audio signal is fed to one of a primarywinding or secondary winding of the transformer, the second audio signalis fed to the other of the primary winding or secondary winding, and thematch signal is provided on a center tap of the primary winding. In thepreferred embodiment, the first audio signal is phase shifted andrectified prior to being fed to the transformer.

An alternative embodiment of the invention includes the steps of, ormeans for: (a) receiving a television signal and demodulating thetelevision signal to obtain a first audio signal, the first audio signalbeing characterized by a first series of zero crossings; (b) generatinga second audio signal on the basis of a signal or sound generated by thetelevision, the second audio signal being characterized by a secondseries of zero crossings; (c) generating a first series of pulses,wherein each pulse in the first series corresponds to a zero crossing ofthe first audio signal; (d) generating a second series of pulses,wherein each pulse of the second series corresponds to a zero crossingof the second audio signal; and (e) generating a match signal on thebasis of the first and second series of pulses, the match signalindicating that the first and second audio signals are from the sametelevision channel. A presently preferred form of the alternativeembodiment receives a television signal on a known channel; increments acounter each time pulses from the first and second series of pulsesoccur simultaneously, and indicates a match when the count value isabove a preset threshold; periodically resets the count value; andchanges the channel from which the television signal is received if amatch is not detected after a prescribed period.

According to another aspect of the invention, a cable televisionaudience monitoring system comprises: a television, a Non-Video PathUnit (NVPU) data collection device for determining the channel to whichthe television is tuned, and a coupler for feeding an input CATV signalto the television and the NVPU.

Other features of the invention are disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are block diagrams of alternative configurations of atelevision metering system in accordance with the present invention.

FIG. 4A and 4B depicts is a block diagram of a presently preferredembodiment of a Non-Video Path Unit (NVPU) data collection device inaccordance with the present invention.

FIG. 5 is a block diagram of an alternative embodiment of the NVPUdevice.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The Non-Video Path Unit (NVPU) 12 is a device which monitors the channelbeing viewed by a cable television viewer. The NVPU 12 performs audiomatching and can be used on a variety of television viewing systems,including but not limited to (1) a television 10 with a direct cableinput line, as in FIG. 1; (2) a television with a set-top converter 14(i.e., a decoder box), as in FIG. 2; and (3) a television with a VCR 16and a set top converter 14, as in FIG. 3. The NVPU 12 can also be usedon other television viewing systems, including those receiving signalsfrom a satellite (not shown).

In one presently preferred embodiment, the outer case (not shown) of theNVPU 12 is plastic with metallic paint to reduce signal radiation andinterference. In this embodiment, the NVPU 12 includes two printedcircuit (PC) boards, including (1) a digital board, or communicationsmodule, and (2) an analog board, also called the "audio matching"module. The two boards are connected by a connector.

The communications module includes a digital signal processor (DSP)controller (item 46 in FIG. 4B); a flash memory EPROM (item 45 in FIG.4B); a modem (not shown); a real time clock connected to a battery (notshown); and a voltage regulator (not shown), which converts 12 V AC to±5 and ±12 V DC. The voltage regulator on the digital board provides allthe DC voltage for the audio matching module. A "Telco" output signal(provided via a telephone interface) is available for remotelyinterrogating the NVPU's stored data. The telephone interface can alsobe employed to provide a telephone number and time (used, e.g., insending the NVPU's stored data), receive time and reset the on-boardclock (discussed below), and receive uploaded software.

FIG. 4A and 4B depicts is a block diagram of one presently preferredembodiment of the NVPU 12. As shown, the broadband cable signal to thetelevision set (or the cable converter or decoder box) enters through acoaxial cable 20 and is passed through a coupler 22 to the NVPU 12. Thecoupler has low loss and a wideband frequency response that covers thefull cable channel spectrum, and provides the entire broadband cablesignal to the NVPU's channel detection circuitry. This circuitryincludes a high pass filter 24 that removes out-of-band signals belowchannel 2; an amplifier 26 (50-450 MHz); a mixer 28 (3.25 MHz output);an IF amplifier 30; and an FM demodulator 32, which outputs an audiosignal 33. The audio signal 33 is fed sequentially to a 90° phaseshifter 34A, lowpass filter 34B, amplifier 34, full-wave rectifier 34C,and an audio comparator 36. The output of the audio comparator is fed toan amplifier 36A, filter 36B, voltage comparator 36C, and then to abuffer 36D. The NVPU 12 also includes an input 38 for receiving audiofrom an audio output of a TV; a peak detector 40 and voltage comparator40A; an optional magnetic pickup 42, which can be used instead of thedirect audio from the TV; a DSP controller 46 coupled to a reset timer47A, clock 47B, flip-flop 47C, and memory (SRAM) 47D; a synthesizer 48;a set of voltage controlled oscillators (VCOs) 50, 52, 54; a band selectswitch 56; another amplifier 58; a prescalar unit 60; a codec(coder/decoder) 62, and a telephone interface 64.

The VCOs 50, 52, 54 generate signals between 248 MHz and 496 MHz. Thehi-band signal is between 248 MHz and 453.25 MHz, and is generated byVCO 50. The mid-band signal is between 124 MHz and 248 MHz, and isgenerated by VCO 52. VCO 54 generates a lo-band signal between 53.25 MHzand 130 MHz. The band select switch 56 selects an output of the VCOs andis controlled by the DSP 46 (although the connection between the DSP andsynthesizer is not shown). The selected 53.25-453.25 MHz signal is thenmixed by the mixer 28 with the incoming audio subcarrier received viathe cable input. The output of the mixer 28 is a 3.25 MHz audiosubcarrier. The 3.25 MHz audio subcarrier is amplified and demodulated,and the audio baseband is recovered and output on line 33 to the phaseshifter 34A. The audio baseband signal on line 33, demodulated from the3.25 MHz audio subcarrier as described above, is phase shifted by 90° byphase shifter 34A, filtered by lowpass filter 34B, amplified byamplifier 34, full-wave rectified by rectifier 34C, and input to audiocomparator 36. Another audio baseband signal from the television 10(FIGS. 1-3) is obtained from the audio cable connected to thetelevision's audio output jack. Alternatively, if there is no outputjack, this other audio signal is obtained from the magnetic pick-up coil42 placed near the television's speaker (not shown). The magneticpick-up 42 is designed not to detect conversation and audio noise notemanating from the television. The audio signal is generated by themagnetic pick-up coil on the basis of the magnetic flux generated by thespeaker of the television set. This audio signal is fed to amplifier 39and then into audio comparator 36. The amplifier 39, peak detector 40,voltage comparator 40A, and buffer 36D are employed to determine whetherthe television set is turned on and emitting sound. The voltagecomparator 40A compares the voltage from the peak detector 40 with apre-set DC voltage, which allows the system to account for ambient noisethat may be present.

The two audio baseband signals (i.e., the audio signal from the cableand the audio signal from the TV) are compared in audio comparator 36 todetermine whether they match. In the presently preferred embodiment, theaudio comparator 36 is an audio transformer comprising a center-tappedprimary winding connected to receive the rectified audio signal from thedemodulator, and a secondary winding connected to receive the audiosignal from the television set. The other side of the secondary windingis grounded. An output signal is taken from the center tap of theprimary winding. This output signal is a rectified (DC) audio signalwhen the audio signal from the cable and the audio signal from the TVare matched (in phase). The center tap of the primary winding providesan unrectified (AC) signal when the two audio signals are not matched.The output signal of the audio comparator 36 is amplified by amplifier36A and fed into an RC network (filter 36B) that provides a DC outputsignal at a level linearly related to the audio output level of thetelevision set. The voltage comparator 36C compares the signal output offilter 36B with a pre-set voltage level, thus permitting the system toaccount for ambient noise.

The prescalar unit 60 divides the signal output by amplifier 58 (e.g.,by 128, 256, etc.) and feeds the divided signal back to the synthesizer48, as a feedback signal for use in accurately synthesizing frequencysignals for the VCOs 50, 52, 54. The flip-flop 47C latches commandsignals from the DSP 46 instructing the synthesizer 48 to tune to aspecified frequency.

Those skilled in the art will recognize that many modifications can bemade to the preferred embodiment without departing from the true scopeof the present invention. For example, the present invention can bepracticed by detecting transitions of the two audio signals, producing apulse for each transition, and comparing the pulses to determine whetherthe signals match. This embodiment is depicted in FIG. 5 and describednext.

As shown in FIG. 5, the broadband cable signal to the television set (orthe cable converter or decoder box) enters through a coaxial cable 120and is passed through a coupler 122 to the NVPU 12'. The coupler couplesthe entire broadband cable signal to the NVPU's channel detectioncircuitry. This circuitry includes a high pass filter 124 that removesout-of-band signals below channel 2; a first amplifier 126 (50-450 MHz);a mixer 128 (3.25 MHz output); a second amplifier 130; an FM demodulator132, which outputs an audio signal 133; a third amplifier 134; an audiomatching detector 136; a series of 8-bit registers 137; an input 138 forreceiving audio from an audio output of a TV; a peak limiter 140; anoptional magnetic pickup 142, which can be used instead of the directaudio from the TV; a comparator 144 coupled to the EPROM 145; the DSPcontroller 146; a synthesizer 148; a voltage controlled oscillator (VCO)150; a first divider 152; a second divider 154; and a band switch 156.

The VCO 150 generates a signal between 248 MHz and 496 MHz. The mid-bandsignal between 124 MHz and 248 MHz is generated in the first divider 152by dividing the VCO signal by 2. The second divider 154 generates asignal between 53.25 MHz and 130 MHz by dividing the mid-band signal.The band switch 156 selects the output of the VCO or one of the dividersand is controlled by the DSP 146. The selected 53.25-453.25 MHz signalis then mixed by the mixer 128 with the incoming audio subcarrier. Theoutput of the mixer is a 3.25 MHz audio subcarrier. The 3.25 MHz audiosubcarrier is amplified and demodulated, and the audio baseband isrecovered and output on line 133 to the third amplifier 134.

Another audio baseband signal from the television 10 is obtained from anaudio cable connected to the television's audio output jack or themagnetic pick-up 142. This audio signal is fed to an amplifier, the peaklimiter 140, and then into the audio matching or zero crossing detector136. The audio baseband signal from the cable, once it has beendemodulated from the 3.25 MHz audio subcarrier, is amplified byamplifier 134 and input into the zero crossing detector 136. The twoaudio baseband signals are compared to determine whether they match.

In this embodiment, the audio baseband signal from the television is fedvia line 138 to the peak limiter 140 and then into the zero crossingdetector 136. A pulse generator circuit in the zero crossing detector136 (which detects transitions from positive to negative voltages andvice versa) produces a 25 microsecond pulse for each transition. Asimilar stream of pulses is generated for the demodulated audio signalfrom amplifier 134. The two streams of pulses are fed to the pulsecomparator 144, which increments a counter each time pulses occursimultaneously. This counter is reset at periodic intervals. A thresholddetector in the comparator circuit 144 indicates when the count value isabove a preset threshold. If, after a fixed period of time, thethreshold detector 144 indicates that the count is above the threshold,a logic HIGH signal is sent to the DSP controller 146 to indicate amatch. If the threshold detector indicates a mismatch between the twoaudio signals, the DSP controller tunes the synthesizer 148 to the nextfrequency (or channel) and will continue to do so until a match isdetected. Specifically, if there is no match, housekeeping logic in theDSP 146 increments a channel counter, resulting in the comparison of theaudio signal pick-up from the television with the next channel on thecable. The channel number is used in association with an EPROM 145look-up table to determine the audio subcarrier frequency being used forthat channel. This frequency information is fed back into thesynthesizer 148 and the audio subcarrier frequency for the new channelis extracted. The NVPU receives guidance information (e.g., whichchannels to look at, audio subcarriers, offset frequency) from theseries of 8-bit registers 137. Through the same 8-bit registers, theNVPU indicates whether the television set is on or off and if theselected channel matches the channel being viewed.

I claim:
 1. A method for determining the channel to which a televisionis tuned, comprising the steps of:(a) receiving a television signalreceivable by a television and demodulating said television signal toobtain a first audio signal; (b) obtaining a second audio signalrepresentative of sound generated by said television as a result ofbeing tuned to one of a prescribed set of channels; and (c) generating amatch signal on the basis of said first and second audio signals, saidmatch signal indicating whether said first and second audio signals arefrom the same television channel; wherein said match signal is generatedby an audio transformer; and wherein said first audio signal is fed toone of a primary winding or secondary winding of said transformer, saidsecond audio signal is fed to the other of said primary winding orsecondary winding, and said match signal is provided on a center tap ofsaid primary winding.
 2. A method for determining the channel to which atelevision is tuned as recited in claim 1, wherein said first audiosignal is phase shifted and rectified prior to being fed to saidtransformer.
 3. A method for determining the channel to which atelevision is tuned as recited in claim 2, wherein said first audiosignal is phase shifted by approximately 90°.
 4. A system fordetermining the channel to which a television is tuned, comprising:(a)means for receiving a television signal receivable by a television anddemodulating said television signal to obtain a first audio signal; (b)means for obtaining a second audio signal representative of soundgenerated by said television as a result of being tuned to one of aprescribed set of channel; and (c) means for generating a match signalon the basis of said first and second audio signals, said match signalindicating whether said first and second audio signals are from the sametelevision channel; wherein said means for generating a match signalcomprises an audio transformer; and wherein said first audio signal isfed to one of a primary winding or secondary winding of saidtransformer, said second audio signal is fed to the other of saidprimary winding or secondary winding, and said match signal is providedon a center tap of said primary winding.
 5. A system for determining thechannel to which a television is tuned as recited in claim 4, furthercomprising a phase shifter, wherein said first audio signal is phaseshifted and rectified prior to being fed to said transformer.
 6. Asystem for determining the channel to which a television is tuned asrecited in claim 5, wherein said first audio signal is phase shifted byapproximately 90°.